A video stream is a stream of image data units that form a stream of video frames. A video frame, also called a frame, is a still image that can be displayed on a video display, e.g., on a liquid crystal display (LCD). Feeding a video stream to a display may cause the display to display the frames of the video stream to give a viewer the impression of a moving image. The number of frames per second provided by the video stream and the number of frames per second displayed by the display are each known as a frame rate.
In a real-time viewing system, a video camera may be operated to generate a source video stream. A video display may be arranged to be driven by the source video stream so as to provide a live view of the scene captured by the video camera. A buffer may be connected between the video source and the video display so as to buffer the source video stream in order to ensure smooth operation of the video display.
An example of a video system 10 comprising a video source 12, e.g., a camera, and a display 14 is schematically represented in FIG. 1. A video processing unit 16 may have an input connected to the video source 12 and an output connected to the display 14 for driving the display in real-time response to the video source 12. The video processing unit 16 may, for instance, comprise a memory unit 18, a buffer control unit 20, and a display control unit 22. The video processing unit 16 may operate as follows. The buffer control unit 20 receives the source video stream from the video source 12 and writes consecutive frames of the source video stream to the memory unit 18 in accordance with a circular buffering scheme. More specifically, the buffer control unit 20 may maintain three frame buffers 19a, 19b, and 19c in the memory unit 18. The buffer control unit 20 may write a first frame to the frame buffer 19a, the next frame (second frame) to the frame buffer 19b, and the following frame (third frame) to the frame buffer 19c. The following frame (fourth frame) may be written to the frame buffer 19a, overwriting the first frame. These operations may be repeated in a cyclic manner. Whenever a frame has been written to one of the frame buffers 19a, 19b, and 19c, it will be remain in the respective frame buffer for a duration of approximately two frames before it is overwritten by a later frame by the buffer control unit 20. The display control unit 22 thus has sufficient time for retrieving a buffered frame from the memory unit 18 before the frame is overwritten by the buffer control unit 20. For example, the buffer control unit 20, upon storing a complete frame in one of the frame buffers 19a to 19c, may provide the display control unit 22 with a control signal informing the display control unit 22 that the respective frame buffer is ready to be read out by the display control unit 22. The display control unit 22 may further feed the frames retrieved from the memory unit 18 consecutively to the display 14 in accordance with a target frame rate, e.g., 60 Hertz. The target frame rate may be substantially equal to the source frame rate, i.e., the frame rate of the source video stream, or it may differ. For example, the display control unit 22 may skip or repeat a frame provided by the frame buffers 19a to 19c. 